Under the overarching theme of human movement variability, in this research proposal; we will target chronic stroke survivors with the objective of defining gait variability measures as sensitive biomarkers of gait adaptation. In addition, the sensitivity of variable visual feedback through Virtual Reality (VR) will be explored in order to maximize gait adaptation in this patient population. Walking, which has inherent variable characteristics, involves the integration of visual, proprioceptive and vestibular sensory information. This information is used to navigate over-ground and to adapt to alterations in the environmental and/or task. Better outcomes during gait rehabilitation of subjects with age-related gait disturbances or with sensorimotor abnormalities as a result of stroke, may be realized by manipulating the visual input instead of the proprioceptive or the vestibular inputs for two reasons. First, in the presence of information from multiple senses, visual input is given precedence. Second, augmented visual inputs during training can help to remove sensory conflicts that commonly exist during gait rehabilitation. In the first aim, stroke survivors will be compared with healthy controls for adapting to a split-belt treadmill paradigm with/without VR. In the second aim, the effect of VR on the transfer of split-belt adaptation to overground locomotion will be investigated. Gait variability measures, as sensitive biomarkers of adaptation and transfer will be investigated. In the third aim, different types of variable visual feedback will be tested for optimizing gait adaptation. Our preliminary studies and previous experiences in the field of virtual reality, gait variability and pathological gait patterns have positioned us well in utilizing this technology for the advancement of neurorehabilitation in the stroke population. In light ofthe effectiveness of various stroke rehabilitation techniques still being controversial, the need for more effective rehabilitation strategies is strongly desired. Virtual technology provides us with the advantage of manipulating the visual environment around the subject through high-tech simulations and also offers the capability to customize the technology to serve the special needs of each patient through restoring healthy patterns of variability and complexity.